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    STUDIA CHEMIA - Issue no. 2 / 2006  
         
  Article:   ELECTROCHEMICAL CHARACTERIZATION OF SANDWICH-TYPE PHOSPHOTUNGSTOCERATE (IV) AND ARSENOTUNGSTOCERATE (IV) IN AQUEOUS AND NON-AQUEOUS SOLUTION.

Authors:  ADRIAN-RAUL TOMŞA, AGLAIA KOUTSODIMOU, POLYCARPOS FALARAS, MARIANA RUSU. 		 
       
         
  Abstract:  The electrochemical properties of two sandwich-type polyoxotungstocerate (IV) [(CeO)3(H2O)2(PW9O34)2]12- and [(CeO)3(H2O)2(AsW9O34)2]12- have been studied by cyclic voltammetry in aqueous and acetonitrile solutions. Voltammograms recorded in aqueous solutions showed the existence of two waves for the Ce(III)/Ce(IV) redox couple. These could be explained by a nonequivalence of the Ce atoms in the polyoxotungstate molecule, where one Ce atom is six coordinated and the other two, are seven coordinated. The presence of only one peak pair for Ce(III)/Ce(IV) suggests the equivalence of these metal ions in the polyoxometalate complexes when isolated as tetrabutylammonium salts. When increasing amounts of LiClO4 have been added to the acetonitrile solutions of the polyoxotungstocerate while keeping the ionic strength constant with 1M [Bu4N]ClO4 a dramatic change of the electrochemical behavior was observed, which was assigned to the association of Li+ ions with the reduced forms of the polyoxometalates.  
         
     
         
         
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